Vibration analysis has been used for years to provide a determination of the proper functioning of different types of machinery, including rotating machinery and rocket engines. A determination of a malfunction, if detected at a relatively early stage in its development, will allow changes in operating mode or a sequenced shut down of the machinery prior to a total failure. Such preventative measures result in less extensive and/or less expensive repairs, and can also prevent a sometimes catastrophic failure of equipment.
One approach to monitoring the health of machinery involves scheduled recording and playback of vibration data over time to provide historical mapping of the machine using frequency and power spectral density analysis. By this process, degradation of machine internal components can be identified. Currently, to record machine vibration data, the output from an accelerometer is conveniently first connected to a signal conditioning module. The conditioned accelerometer signal is then recorded either on digital magnetic tape, analog magnetic tape, or a digital computer system with large random access memory. Alternatively, a spectrum analyzer may be periodically transported to the machine under observation for direct measurements.
The current method for obtaining machine vibration information thus requires the use of bulky and expensive instrumentation. It is difficult to transport such sophisticated equipment without increasing the already substantial cost of maintenance of such equipment. There is also a significant amount of lost labor time incurred due to the difficulties of transporting relatively fragile and bulky instrumentation.
U.S. Pat. No. 4,977,516 to J. E. Shepherd discloses a data acquisition device which has the capability to receive input simultaneously from a plurality of vibration sensors using a microprocessor which stores and processes the data collected. One problem with such data acquisition devices is the need to digitize data prior to storing it. Digitized data requires a large amount of memory for storage and requires additional circuitry. Also problems exist where multiple analog inputs are needed because they are typically multiplexed prior or subsequent to digitizing. Since the machine is rotating, compensation must be made for the fact that measurement signals may not actually be taken simultaneously, and are generally taken at different points during the shaft rotation due to the multiplexing. Such a system requires additional software/hardware to compensate for the time delay which otherwise may result in the loss of desired information. As an example of such compensation, U.S. Pat. No. 4,608,650 to N. S. Kapadia uses non-recursive tracking digital filtering to determine a peak velocity or displacement of the rotating engine for processing sampled accelerometer data. In a different operating phase, the Kapadia apparatus determines the rotational location of the peak relative to an index or reference point on the rotating engine.
U.S. Pat. No. 4,453,407 to Sato et al. discloses a sophisticated system which may be difficult and bulky to transport for on-site vibration analysis.
U.S. Pat. Nos. 4,313,178 to Stern et al., 4,989,179 to R. T. Simko, and 4,627,027 to Rai et al., disclose solid state analog memory elements but do not disclose circuitry for recording of accelerometer information. Although R. T. Simko suggests that his analog memory storage element may be used to record vibration, he does not disclose how this should be accomplished.
The presently available accelerator recording and analysis systems provide valuable information, but they are bulky and expensive. Consequently, a need exists for improvements in accelerometer recording devices to decrease their high cost, as well as their complexity and difficulties of transportation logistics. Those skilled in the art have long sought and will appreciate the novel features of the present invention which solves these problems.